Broadleaf Forests

The forests of the Chatham Islands are relatively low as none of the taller trees of the New Zealand mainland are present. There are no conifers at all, no beeches (Nothofagus), nor any of the other canopy dominants such as tawa (Beilschmiedia tawa), kamahi (Weinmannia racemosa), hinau (Elaeocarpus dentatus), or northern or southern rata (Metrosideros robusta, M. umbellata). In more open sites a notable absentee is the cabbage tree (Cordyline australis).

On steeper slopes, too well drained to permit the development of peat, the forest is relatively rich in species. A close canopy at 6 to 13m is dominated by endemic species: Coprosma chathamica (the largest species of the genus), Pseudopanax chathamicus, Melicytus chathamicus, Myrsine chathamica, the striking yellow-flowered Brachyglottis (Senecio) huntii, and on more fertile soil the nikau palm, Rhopalostylis sapida.

Among the few understory species are kawakawa (Macropiper excelsum) and tree ferns, particularly Dicksonia squarrosa and D. fibrosa. The common vines are supplejack (Ripogonum scandens) and Muehlenbeckia australis. A number of epiphytes are present including the fern Pyrrosia serpens and the orchids Earina mucronata and E. autumnalis, but there are no asteliad nests.¹⁷² This type of forest is now restricted to gullies in the south of the main island (Fig. 118) and the southern part of Pitt Island.

On more or less level sites in the lowlands, karaka (Corynocarpus laevigatus) dominated where drainage was good, giving way to Plagianthus regius var. chathamicus on the most fertile soils and to Sophora microphylla on calcareous sediments. On coastal cliffs and some dune country Olearia traversii played a similar role to that of pohutukawa (Metrosideros excelsa) in the northern North Island. In swampy situations there was a distinctive forest of this species in combination with Coprosma chathamica. These forest types have been almost entirely cleared for farming.

Plant communities associated with bogs (Fig. 119) are restricted to the main island and these are mostly found on gentle slopes at higher elevations where rainfall is high and mists frequent.

page 214